Method of making glass to metal seals



PatentedFeb.13i,l940 V b V x u V 2 189 970h 1 UNITED STATES: PATENT. OFFICE Stanton Umbreit, West Orange, N. 1., assignor, by

mesne assignments, .to Radio Corporation of 7 "America, New York, N. Y., a corporation 1 Delaware Y lilo Drawing; Application Oetober'Sl, 1937,

Serial No. 1'l2,055

. 2 Claims. (Cl. 49-81) My invention relates to glassto metal seals, formation may in some casesoccur at temperaparticularly to the manufacture of metal alloys, tures between 0 C. and +50 C. i t which have predetermined coemcients of thermal The alloy in the austenitic state when cooled expansion and which will readily seal with glass. several hundred degrees from an elevated tem- 5 In sealing glass to metal,.it is desirableto se perature contracts rapidly; at a rate of about 5 lect the glass and the metal; with coefllcients or 16 10 centi ete pe ce m p r des ee thermal expansion which substantially coincide 0., and at a temperatureof between 400 and 500 or match over the entire temperature range from C. the rate of contraction is reduced to about room to glass softening temperature. cobalt 3.5x centimeters per centimeter per degree C.

10 nickel-iron alloys of the type disclosed in the As the cooling continues to about '0' C.,the"l0 U. S. patent to Burger and Hull, 2,071,196, Febaustenitic state of the alloy abruptly changes to rua'ry 16, 1937, have expansion characteristics the martensitic state with anactual increase in which adapt them for sealing with commercial volume; Further cooling continues contraction bore-silicate glass. It has been found; however, at the rate of about 9x 10- centimeters per centithat in commercial production of these alloys the meter per degree C. I If the metal is now heated, it 1 expansion characteristics of the alloys may'vary expands at the rate of 9x10 until a temperawithin limits and render sealing with a given ture of 500 C. is reached, when the martensite glass difflcult. When an alloy of this kind is gradually changes to austenite with a decreasein formed by pressing or drawing'into the desired volume. It appears that at temperatures above 2 shapes, such as small thin walled cylinders or about 700 C., the alloy is in the austenitic state eyelets for sealing with glass, it appears to vary irrespective of its crystal or grain structure below in crystal or grain structure and in coeillcient that temperature. According to my invention,

of expansion. l the temperature at which the alloy may change An object of my invention is to make glass to from the austenitic to the martensitic state is metal seals in which the coeflicient of thermal exlowered to a temperature below any temperature 5 pansion of the glass and the metal match encountered in manufacture or use so that the throughout the temperature range from room to alloy retains its coefficient of thermal expansion sealing temperature of the glass. of 3.5x 10- below sealing temperature.

A further object of my invention is to'make According to my invention, the. temperature at a stable alloy which will not change in crystal or which the e austenitlc alloy is transformed or 30 grain structure.'and which has a coeflicient of changed into martensitic alloy is w r to a thermal expansion such that it will seal readily point well below temperatures encountered in with commercial glasses. manufacture or use of the alloy. By adding about An alloy in extensive commercial use for seal- .05% or more carbon to the solid solution of the ing with glass, and consisting 01' about 18% coalloy. the r n form n t mpe m be 35 belt, 30% nickel, and the remainder iron when lowered to below --200 C.. the ry al Structure first alloyed, appears to consist or austenite. This f h alloy e m e. a d yelets r wn n' when draw-11mm m n g eyelets and from the alloy retain a constant coefficient of needed appears under the microscope to have the thermal expansmn d 5 readily wlth glassregular twinned polygonal crystals similar to the 9 glass commercially known as 40 gamma phase of iron. 'It has been found, howhard glass h a icoemcxient of thermal ever, that when this alloy is drawn and is.also pension of about 4'5X10 8 per degree cooled to a temperature of about 0 C. the crystal 1 prises 65% ($102) 23% (B203) 77 sodium oxide (NazO) and 5% aluminum ox- 0 a t structure suddenly changes, the shape of crys- 1d (A120) d be d t 1 1 d t 4r tals being irregular and the individual grains bee may a van ageous y sea 6 o o my improved alloy comprising 18% cobalt (Co), 1ng needle-like and resembling martenslte Or the v nickeliron about 0 I, 0 alpha Phase when this transmrmitm 105% carbon in some solution with the alloy. The of crystal structure occurs, the body of the alloy alloy may compriseby weight f 5 ,5

suddenly expands. The coeflicient of thermal exn 23 to 30 nickel and 13 t 25 cqbam p ns o of t e ccbalt-nickel-iren alley in the The thermal expansion characteristic of this glass amma phase may be abo t to X D and alloy is substantially uniform at about degree C., whereas after the transformation, the 4.5 10-r from below room to sealing temperacoefficient of thermal expansion may be of the ture. x

order of 8 to 9.5 10 per degree C. This trans- While the specific example of glass and alloy 55' matching in thermal expansion characteristics has been given, it will be apparent to those skilled in the manufacture of'glass tometal seals that changes in the glass may be made to change its coeihcient of thermal expansion and that corresponding changes may be made in the alloy to bring the thermal expansion characteristics into coincidence.

I prefer, according to one embodiment of my invention, to prepare an alloy of cobalt, nickel, and iron in the proportions above mentioned and to form sealing members or bodies such as cylinders or eyelets from sheets of the alloy. The sealing bodies are then treated, according to my invention,'by diffusing into" the bodies pure carbon preferably by carburizing the parts at a high temperature. Good results have been obtained by heating eyelets of the cobalt-nickel-iron alloy in an atmosphere of hydrogen with a graphite block for minutes at 1100 0. Alternatively, the eyelets may be heated in hydrogen. containing hydro-carbons such as xylene or light oil to difluse carbon throughout the body of the eyelets. I have lower is the transformation temperature. The amount of carbon difl'used into the alloy, however, is limited by the presence of carbon on the sealing surface of the alloy bodies. According to a further feature of my invention, I introduce an excess of carbon or saturate the alloy with carbon and then remove the carbon at the sealing surface of the alloy body by heating in an atmosphere of wet hydrogen.

I claim:

l. The method of sealing a glass with a predetermined coeiilcient of thermal expansion to a metal body of predetermined shape of an alloy of to 54% iron, 28% to 30% nickel and 18% to 25% cobalt, comprising working said alloy to form the body of said shape, diffusing carbon through said body at an elevated temperature to lower the temperature of transformation of the alloy from the austenitic to the martensitic state and, placing said glass in contact with said body, and heating to the sealing temperature. a

2. The method of sealing a glass with a predetermined coeflicient of expansion to a preformed metal body of an alloy of iron, nickel, and cobalt, comprising working the alloy to form said body, heating said body in the presence of carbonaceous gas to introduce more than .05% carbon into said alloy, removing the carbon on the surface of said body, and placing said glass in contact with said body and heating to sealing temperature.

STANTON ULIBREIT. 

